SuperSTEM Access for advanced electron microscopy studies of magnetic nanocomposite materials

纳米材料的合成和表征是一个非常令人兴奋的新兴研究领域，受到了重要的科学和技术关注。纳米材料可以是颗粒尺寸在纳米范围内的块状材料或单独的纳米颗粒。纳米颗粒的大表面积与体积比意味着其性能可能与相应的常规材料显著不同。磁性显示出对颗粒尺寸的显著依赖性。随着颗粒尺寸的减小，铁磁畴壁的形成变得不利，并且发生超顺磁性。纳米粒子阵列可以排列成二维和三维结构，其电学、光学、输运和磁学性质取决于纳米粒子之间的相互作用。分散在保护介质中的纳米颗粒称为纳米复合材料，由两相组成：纳米颗粒（分散相）和防止直接接触的基质（保护介质）。这种纳米复合材料产生有趣的磁，电和催化性能取决于分散相和基质相之间的比例。例如，将存在从磁隔离到相互作用行为的过渡。主要挑战之一是表征纳米材料的形态、表面和原子结构，这是其技术性能的关键。然而，由于纳米材料的颗粒尺寸小，常规技术可能受到限制。例如，随着粒度减小，纳米晶粉末的X射线衍射（XRD）谱演变为类似于非晶样品。需要补充使用不同的结构表征技术。此外，大多数标准技术测量整个样品的平均值，并且不能区分不同的纳米颗粒或单个纳米颗粒的不同区域。非常需要提供纳米颗粒的结构和组成均匀性的纳米尺度分析，这会强烈影响它们的行为。例如，具有氧化物基质的纳米复合材料中的金属颗粒通常具有表面氧化物层，其可以减少有效铁磁体积。为了理解这种现象，需要识别表面氧化物及其厚度。理想地适合于这个问题的是先进的电子显微镜技术，它可以探测纳米级区域，通过高分辨率电子显微镜（STEM）或成分，通过电子能量损失谱（EELS）揭示结构信息。这项建议的目的是应用先进的电子显微镜技术的STEM和EELS这是可用于SuperSTEM设施研究纳米复合材料含有Fe/Co合金和氧化物纳米粒子。

The synthesis and characterisation of nanomaterials is a very exciting emerging field of research which has received important scientific and technological attention. Nanomaterials can be found as bulk materials with grain size in the nanometer range or as separate nanoparticles. The large surface-to-volume ratio of nanoparticles means properties can differ significantly from those of the corresponding conventional materials. The magnetic properties show a dramatic dependence on particle size. As the particle size decrease, the formation of ferromagnetic domain walls becomes unfavourable, and superparamagnetism occurs. Arrays of nanoparticles can be arranged in two- and three-dimensional structures, whose electric, optical, transport and magnetic properties depend on the interaction between nanoparticles. Nanoparticles dispersed in a protective medium are called nanocomposites, and consist of two phases: the nanoparticles (dispersed phase), and the matrix (protective medium), which prevents direct contact. Such nanocomposites yield interesting magnetic, electric and catalytic properties depending on the ratio between the dispersed and matrix phases. For example, there will be a transition from magnetically isolated to interacting behaviour. One of the main challenges is characterising the morphology, surface and atomic structures of nanomaterials, which are keys to their technological properties. However, conventional techniques may be limited for nanomaterials due to the small particle size. For example, X-ray diffraction (XRD) spectra of nanocrystalline powders evolve to resemble an amorphous sample as particle size decreases. The complementary use of different structural characterisation techniques is needed. Furthermore, most standard techniques measure an average over the whole sample, and cannot distinguish between different nanoparticles, or different regions of a single nanoparticle. There is a great need to provide nm-scale analysis of the structural and compositional homogeneity of the nanoparticles, which can strongly affect their behaviour. For example, metallic particles in nanocomposite materials with oxide matrices often have a surface oxide layer which can reduce the effective ferromagnetic volume. To understand this phenomena requires identifying the surface oxide and its thickness. Ideally suited to this problem are advanced electron microscopy techniques which can probe nm-scale regions to reveal information on structure, via high resolution electron microscopy (STEM), or composition, via electron energy loss spectroscopy (EELS). The aim of this proposal is to apply the advanced electron microscopy techniques of STEM and EELS which are available to the SuperSTEM facility to study nanocomposites containing Fe/Co alloy and oxide nanoparticles.